Figure 1: Temporal variations of annual deposition fluxes of ¹³⁷Cs and ^239,240Pu observed at Tokyo (1986 - 1980) and Tsukuba (1980 - ). Red arrows show Chinese thermonuclear tests (21^st : 4 Mt, Nov. 1976; 26th : 0.6 Mt, Oct. 1980). Green arrow shows the Chernobyl accident.